The knee joint includes three bones, namely the femur, tibia and patella. The distal end of the femur lies adjacent to the proximal end of the tibia while the patella lies adjacent the anterior portion of the femur. The joint elements that engage one another are preferably covered by articular cartilage. Specifically, the distal end of the femur and the proximal end of the tibia are covered by articular cartilage, as is the posterior surface of the patella.
The articular cartilage of the knee joint may become damaged due to degeneration and/or wear, which may lead to bone-to-bone contact during articulation of the joint. This may result in significant pain and potential damage to the bone surfaces. A knee replacement procedure may be required in cases where damage to the articular cartilage is significant. Depending on the extent of the damage, the procedure may include at least partial replacement of one or more bones of the knee joint. For instance, in a total knee replacement each of the bones of the knee joint is at least partially covered by implants. In other instances, a knee arthroplasty procedure may be limited to portions of one of the joints. For instance, a patellofemoral procedure is limited to at least partial replacement of the engagement surfaces between the femur and the patella.
The distal femur includes medial and lateral compartments which make up the tibiofemoral joint (“TFJ”) and the patellofemoral compartment which makes up the patellofemoral joint (“PFJ”). The PFJ more specifically includes the patella and the trochlear groove of the femur, and the TFJ includes the lateral and medial condyles of the femur and the tibial plateau.
A number of diseases and injuries may affect the articular cartilage within any or all of these compartments. Some of these conditions may include osteoarthritis, rheumatoid arthritis, genetic defects and/or traumatic injuries. These conditions can lead to severe pain and functional limitations that may reduce a sufferer's quality of life.
Where the damage affects the PFJ and either the lateral or medial compartments of the TFJ, a total knee arthroplasty (“TKA”) or a bicompartmental knee arthroplasty (“BKA”) may be indicated. A TKA typically removes bone within all three compartments and seeks to replace the articular surfaces of these compartments with a series of implants. A TKA may be an option of last resort in that it often results in the removal of at least one or both of the cruciate ligaments, which may reduce proprioception and natural, functional performance. Additionally, TKA is near the end of the spectrum of joint replacement options. Thus, a TKA may eliminate the flexibility of taking a gradual approach of replacing bone as the need arises.
In contrast, a BKA may leave the cruciate ligaments and the lateral or medial condyle intact with the option of receiving a TKA in the future if warranted. BKA's that resurface the PFJ and one compartment of the TFJ often resurface each compartment separately. Thus, the surgeon may perform a patellofemoral arthroplasty followed by a unicondylar arthroplasty. An example of a patellofemoral arthroplasty can be found disclosed in U.S. Provisional Application No. 61/768,765 and an example of a unicondylar arthroplasty can be found in U.S. Pat. No. 8,377,069, the disclosures of which are hereby incorporated by reference herein in their entirety.
Given the close proximity of the TFJ and PFJ compartments, impingement of the resected surfaces that receive the prostheses is cause for concern as it may interfere with a precise fit and functioning of the implants. Current resection guide instrumentation may make it difficult for the surgeon to visualize the size and spread of a unicondylar implant prior to making a distal femoral resection, which may inhibit precise sizing and locational placement of the implant. Further, this instrumentation makes it difficult to visualize the location of the resections for the unicondylar implant with respect to resections for a patellofemoral implant prior to making the required distal cut, which may increase the risk of impingement.